1. Field of the invention
The present invention relates to an electroluminescent device (hereinafter referred as "EL device") having an emitting layer made of an emitting substance, which utilizes an electroluminescence phenomenon that is the emission of light resulting from application of an electric field or the electrons to the substance. More particularly, it is concerned with an organic EL device comprising an anode, a positive-hole transport layer made of an organic compound, an emitting layer made of both an organic compound, and a cathode, and the same EL device further comprising an electron transport layer interposed between the cathode and the emitting layer.
2. Description of the prior art
As organic EL devices, there have been known a device of two-layer structure type having two layers made of organic compounds respectively as shown in FIG. 1, in which an organic fluorescent thin film 3 (hereinafter referred as "emitting layer") and an organic positive-hole transport layer 4 are laminated with each other and are arranged between a metal cathode 1 and a transparent anode 2. There have been also known a device of three-layer structure type having three layers made of organic compounds respectively as shown in FIG. 2, in which an organic electron transport layer 5, an emitting layer 3 and an organic hole transport layer 4 are laminated in sequence and are sandwiched as a whole between a metal cathode 1 and a transparent anode 2.
The hole transport layer 4 facilitates the infusion of the holes from the anode and blocks electrons. The electron transport layer 5 facilitates the infusion of electrons from the cathode.
In these organic EL devices, a glass substrate 6 is furnished outside the transparent anode 2. The recombination of electrons injected from the metal cathode 1 and the holes injected from the transparent anode 2 to the emitting layer 3 generates excitons. The excitons emit light when they are deactivated through radiation. This light radiates toward outside through the transparent anode 2 and the glass substrate 6.
However, there is not combination of materials for the emitting layer have a sufficient luminance and a long life time of emission yet, even though there is an organic EL device comprising an emitting layer made of a pyran compound (this is so called "DCM"), for example, radiating red light with a comparably high luminance. There is a demand for an EL device capable of a high luminance emission.
The present invention has been made to meet such a demand. An object of the invention is therefore to provide an organic EL device capable of emitting light at a high luminaries and achieving a long time life emission.